there is no simple answer to the question "Is college worth it?" Some degrees pay for themselves; others don't. American schoolkids pondering whether to take on huge student loans are constantly told that college is the gateway to the middle class. The truth is more nuanced, as Barack Obama hinted when he said in January that "folks can make a lot more" by learning a trade "than they might with an art history degree". An angry art history professor forced him to apologise, but he was right.

College graduates aged 25 to 32 who are working full time earn about $17,500 more annually than their peers who have only a high school diploma, according to the Pew Research Centre, a think-tank. But not all degrees are equally useful. And given how much they cost—a residential four-year degree can set you back as much as $60,000 a year—many students end up worse off than if they had started working at 18.

PayScale, a research firm, has gathered data on the graduates of more than 900 universities and colleges, asking them what they studied and how much they now earn. The company then factors in the cost of a degree, after financial aid (discounts for the clever or impecunious that greatly reduce the sticker price at many universities). From this, PayScale estimates the financial returns of many different types of degree (see chart).